Lately, as a lightweight and thin panel illuminant having excellent flexibility in shape, an organic dispersion EL panel is attracting attention among other EL panels (electroluminescent panels). Such an organic dispersion EL panel is extensively used as a backlight for various types of liquid crystal display devices and other various types of display boards such as LCD modules like PDA (personal digital assistant) handy terminals, and for a variety of other uses.
The organic dispersion EL panel has the following configuration. A light emitting layer is configured by having fluorescent particles of ZnS or the like dispersed into an organic polymer. A back electrode made of an Al foil or the like is laminated on one of the surfaces of the light emitting layer with a reflective insulating layer intervened between them. A transparent electrode sheet, which has a transparent electrode made of an ITO deposited film or the like formed on a transparent insulating film, is laminated on the other surface of the light emitting layer. External extension leads are respectively fitted to both the back electrode and the transparent electrode sheet. The lead for the transparent electrode is pressure-welded to a power feed portion, which comprises an Ag paste-applied layer formed on the transparent electrode sheet. The laminate having the layers described above is sealed with a package film to form an organic dispersion EL panel.
Meanwhile, portable compact information terminals such as handy terminals are spreading these days. Demands for a miniaturized liquid crystal display device to be used for such portable compact equipment are increasing. The EL panel used as a backlight for such a small liquid crystal display device is demanded to be made small and thin. Consequently, a EL panel having a thickness of about 0.6 to 0.7 mm is also becoming the mainstream. The EL panel is further tried to be decreased in the thickness.
However, there has occurred a new problem. Specifically, the organic dispersion EL panel applies an alternate voltage to between the transparent electrode and the back electrode to emit light. Therefore, the organic dispersion EL panel produces very small oscillations due to a cycle of polarity inversion of the alternate voltage. On the other hand, where the EL panel is built in as the backlight of an LCD cell or the like, a gap of 1 mm or below is generally between the LCD cell and the EL panel. Very small oscillations may cause resonance in the gap between the LCD cell and the EL panel because of the polarity inversion of the EL panel. It was found that the resonance phenomenon might cause noise from the LCD cell surface.
As means for preventing the EL panel from oscillating, there is known a technique of forming a copper plate on the outside of the back electrode to give an equal potential to the transparent electrode and the copper plate. This three-electrode structure can theoretically eliminate oscillations caused due to the cycle of polarity inversion of the alternate power. But, the oscillation preventing technique, which further adds the copper plate, naturally sacrifices a thickness of the EL panel. Accordingly, in the recent EL panel which is particularly required to be made very thin, the oscillation preventing technique described above cannot remedy noise.
Further, as means for preventing oscillations of the EL panel, an oscillation preventing film may be used, or the EL panel may be fixed to a high rigid substrate. But, such oscillation preventing means involve the increase of a thickness of the EL panel. Therefore, such means cannot be applied at all to the recent EL panels which are demanded to be made very thin.
Accordingly, there is highly demanded for a technique which prevents oscillations caused due to the cycle of polarity inversion of the alternate voltage without adding a particular structure to a conventional EL panel. And, it is demanded to prevent the oscillations of the EL panel and its resonance in the gap between the LCD cell and the EL panel, thereby reducing noise from the LCD cell surface resulting from them.
An object of the present invention is to provide an EL panel which can prevent oscillations due to a cycle of polarity inversion of an alternate voltage without involving the increase or the like of a thickness of the EL panel. Another object of the invention is to provide an LCD module which can reduce noise derived from oscillations of the EL panel. An EL panel package film and its production method of the present invention were achieved in order to prevent the oscillations described above.